Large-Airfoil-Model

Large Airfoil Model

You can access the Large Airfoil Model as well as the details about ASPIRE and ADAPT on our Large Airfoil Model website. The following readme only contains information on the ASPIRE database.

ASPIRE - Airfoil Surface Pressure Information Repository of Experiments

ASPIRE is an open-source database accessible to the wider aerospace community utilizing the vast, nearly century-old historical repository of experimental airfoil data. It was first released on Nov. 11, 2024 in a paper titled Large Airfoil Models.

The database was established through an extensive data mining operation for strictly experimental pressure distributions for a variety of airfoils. Each entry of ASPIRE consist of experimental $C_p$ measurements for various airfoil geometries, angles of attack ($\alpha$), chord-based Reynolds numbers ($Re$), and Mach numbers ($M$). The complete list of fully digitized as well as those in progress can be found here.

Available Data

ASPIRE consists of 2141 unique pressure distributions from 61 airfoils from various airfoil families and applications. All profiles of the airfoils included in the database, compared against the commonly studied NACA 0012, is shown below. Airfoil profiles thicker than a NACA 0012 at the given chordwise location are colored in varying shades of red. Profiles thinner than the NACA 0012 are colored in shades of blue.

<img src="Figures/2_all_af-1.png" width=40% height=40%>

Geometric profiles of all airfoils in the database colored by their thickness compared to the baseline airfoil of NACA 0012

The available data ranges from $-30^{\circ}$ to $30^{\circ}$ in angles of attack ($\alpha$). The Mach number ($M$) of the data spans $0.0$ to $1.0$, from the incompressible regime to transonic and sonic regimes. The number of available pressure data in terms of unique airfoils at a given $M$ and $\alpha$ is shown in below. The color and the number in the center plot denotes the number of unique airfoils available for a given $M$ - $\alpha$ combination. Marginal histograms are plotted to provide a clear visualization of the available data at specific $\alpha$ or $M$. These are split in terms of airfoil families, design usage, and supercriticality.

<img src="./Figures/2_avail_data_family-1.png" width=60% height=50%>

Distribution of available airfoil pressure data and the marginal histograms categorized by airfoil family

<img src="Figures/2_avail_data_family-1.png" width=60% height=50%>

Distribution of available airfoil pressure data and the marginal histograms categorized by airfoil usage

<img src="Figures/2_avail_data_family-1.png" width=60% height=50%>

Distribution of available airfoil pressure data and the marginal histograms categorized by supercritical airfoil

Last updated on 7/31/2024

Data Format

Each airfoil folder should contain 3 types of files: the coordinate file (csv), pressure data files (csv), and tag file (json).

Coordinates File

The coordinate files will define the geometry of the airfoil, with the first column being the normalized chordwise location ($x/c$) and the second column being the normalized thickness ($y/c$) as seen below. The order of the coordinates should start from the upper surface of the trailing edge ($x/c = 1.0$) to the leading edge ($x/c = 0.0$) and end at the lower surface of the trailing edge ($x/c = 1.0$). The coordinate files should be named: <airfoilname>_coordinates.csv.

<img src="Figures/coord_explained.PNG" width=60% height=50%>

Visualization of airfoil coordinates file format

Pressure File

Each CSV file consists of the airfoil pressure measurements along the entire wing chord at a given angle of attack and Mach number. The file should following the naming scheme of <airfoilname>_A<angle of attack> _M<Mach number>_Re<Reynolds number>_A.csv. A negative angle of attack should have an “m” in front of the angle attack to denote the minus sign. For a NACA0012 airfoil at $\alpha = -2.1^\circ$, $M = 0.3$, and $Re = 3.0 \times 10^6$ would have the file name NACA0012_Am2.1_M0.30_Re3e6_A.csv.

Just like the coordinates file, the first column corresponds to the normalized chordwise location ($x/c$) in the same order of Upper TE → LE → Lower TE. The second column is the pressure coefficient at the given chordwise location. The very first entry denotes the Mach number of the experiment. This format is visualized below.

<img src="Figures/cp_explained.PNG" width=60% height=50%>

Visualization of airfoil pressures file format

Tag File

In many sources, the experimental accuracy are reported by the authors within an report. These are often reported as a single scalar value in terms of the maximum magnitude of the error, or the maximum percentage error. These values were recorded in the ASPIRE in an accompanying tag file. Additionally, if the uncertainties in the independent variables such as those of the freestream Mach number, angles of attack, or pressure sensor locations were found in references, they were also reported in the tag files. An example of the tag file included in the database can be seen in below.

<img src="Figures/2_tags-1.png" width=60% height=50%>

Format of tag files found for each experiment in ASPIRE

Getting Started

Download

To access all airfoil experimental data in ASPIRE, run the following:

git clone https://github.com/hwlee924/Large-Airfoil-Model.git
cd Large-Airfoil-Model

How to contribute

Refer to the here to identify a data source that needs to be digitized and request edit access. If you have a specific document that you would like to work on that is not on the file, add an entry to the spreadsheet.

Please ensure that the data adheres to the format outlined in the previous section. For guidance on how to digitize publicly available experimental data, please refer to the Experimental Data Digitization section.

Experimental Data Digitization

Sources

There are largely three ways that I have been using to obtain experimental airfoil pressure data: Google Scholar, Aerospace Research Central (ARC), and NASA Technical Reports Server (NTRS).

  1. Google Scholar: In Google Scholar, you can essentially “google” existing papers. Use appropriate key words such as “airfoil pressure distribution”, “wind tunnel investigation”, etc. to find a wide variety of existing papers from different sources. Most of these will involve graphical plots of pressure data.
  2. Aerospace Research Central: ARC is hosted by AIAA and will give you papers that they have hosted in AIAA conferences and journals. If you are part of an academic institution, you should likely have access to the database. The website is more focused than Google Scholar but has a good variety of all aerospace-related literature. As with Google Scholar, most of these will involve graphical plots of pressure data.
  3. NASA Technical Reports Server: NTRS specifically hosts NASA’s technical reports. While these documents are often very old, they also provide the most extensive coverage of a variety high quality airfoil experiments. Most of the data has a combination of tabulated and graphical results. This lets you verify your digitization relatively easily. However, due to the age of many documents, the quality of the scanned PDFs may be poor.

Digitizing Tabulated Data

If the source material presents the experimental data in a tabulated format, I recommend that you use Optical Character Recognition (OCR) tools available online. Personally, I got best results from ExtractTable.

The workflow of using an OCR tool of your choice is as follows:

Digitizing Graphical Data

If the source material presents the experimental data in a graphical format (plot), I recommend that you use the online tool WebPlotDigitizer.

The workflow of using WebPlotDigitizer is as follows:

Notes